Mysql server won't work when using another data directory

Question

I have an amazon ec2 instance running on Amazon Linux AMI. I'm trying to move the data directory for mysql on a second volume (mounted on /home/ec2-user/data ) with following config file ( /etc/my.cnf ) but mysql fails to start:

[mysqld]
datadir=/home/ec2-user/data/mysql
socket=/home/ec2-user/data/mysql/mysql.sock
log-bin=/var/log/mysql/mariadb-bin
log-bin-index=/var/log/mysql/mariadb-bin.index
symbolic-links=0

[mysqld_safe]
log-error=/var/log/mysqld.log
pid-file=/var/run/mysqld/mysqld.pid

[client]
port=3306
socket=/home/ec2-user/data/mysql/mysql.sock

I get these error messages in the log file:

2017-10-12 14:06:33 20082 [ERROR] Can't open the mysql.plugin table. Please run mysql_upgrade to create it.
2017-10-12 14:06:33 20082 [ERROR] Can't start server : Bind on unix socket: Permission denied
2017-10-12 14:06:33 20082 [ERROR] Do you already have another mysqld server running on socket: /home/ec2-user/data/mysql/mysql.sock ?
2017-10-12 14:06:33 20082 [ERROR] Aborting

When I set the config file back to former settings (to the backup of the data folder) everything works fine:

[mysqld]
datadir=/var/lib/mysql.bak
socket=/var/lib/mysql.bak/mysql.sock

log-bin=/var/log/mysql/mariadb-bin
log-bin-index=/var/log/mysql/mariadb-bin.index
symbolic-links=0

[mysqld_safe]
log-error=/var/log/mysqld.log
pid-file=/var/run/mysqld/mysqld.pid

[client]
port=3306
socket=/var/lib/mysql.bak/mysql.sock

What could be the cause of this problem? I've already checked for the permissions on the new data folder but that doesn't change anything.

Answer 1

Run this command:

chgrp -R mysql /home/ec2-user/data/mysql
chown -R mysql /home/ec2-user/data/mysql

Can you try the following config file ?

[mysqld]
datadir=/home/ec2-user/data/mysql
socket=/var/lib/mysql.bak/mysql.sock

log-bin=/var/log/mysql/mariadb-bin
log-bin-index=/var/log/mysql/mariadb-bin.index
symbolic-links=0

[mysqld_safe]
log-error=/var/log/mysqld.log
pid-file=/var/run/mysqld/mysqld.pid

[client]
port=3306
socket=/var/lib/mysql.bak/mysql.sock